This invention relates to an automatic transmission with a planetary gear unit (planetary gear speed change mechanism) for use in vehicles such as automobiles and, more particularly, to a planetary pinion of the planetary gear unit.
Referring to FIG. 1, an automatic transmission 1 has an input shaft 12 through which a torque output from a torque converter is input. The automatic transmission 1 also has an overdrive planetary gear unit 13 connected to the input shaft 12, and a main transmission unit 16 having a front planetary gear unit 14 and a rear planetary gear unit 15.
The overdrive planetary gear unit 13 includes a carrier 18 which is connected to the input shaft 12 and on which a planetary pinion 17 is supported, a sun gear 19 encircling the input shaft 12, and a ring gear 21 connected to an input shaft 20 of the main transmission unit 16.
The front planetary gear unit 14 has an output shaft 22, a carrier 24, a sun gear 25a and a ring gear 26, and other members. The rear planetary gear unit 15 has a planetary pinion 27, a sun gear 25b, a carrier 28, a ring gear 29 and other members.
An overdrive direct clutch C.sub.0 and a one-way clutch F.sub.0 are provided in parallel with each other between the carrier 18 and the sun gear 19. Power transmission between the carrier 18 and the sun gear 19 is effected through the overdrive direct clutch C.sub.0 when the overdrive direct clutch C.sub.0 is actuated, or power is transmitted in one direction alone through the one-way clutch F.sub.0 when the overdrive direct clutch C.sub.0 is not actuated. An overdrive brake B.sub.0 is provided between the sun gear 19 and a case 6.
The carrier 24 of the front planetary gear unit 14 is connected to the output shaft 22 and supports a planetary pinion 23. The sun gear 25a of the front planetary gear unit 14 is integrally combined with the sun gear 25b of the rear planetary gear unit 15 by a connecting member 25 which encircles the output shaft 22. The ring gear 26 of the front planetary gear unit 14 is connected to the input shaft 20 through a forward clutch C.sub.1. A direct clutch C.sub.2 is provided between the input shaft 20 and the sun gear 25a, and a second coast brake B.sub.1 consisting of a band brake is provided between the sun gear 25a and the case 6.
A second brake B.sub.2 which is of a multi-plate type is provided between the sun gear 25a and the case 6. A one way clutch F.sub.1 is connected between the second brake B.sub.2 and the sun gear 25a.
The rear planetary gear unit 15 includes the carrier 28 on which the planetary pinion 27 is supported, the sun gear 25b, and the ring gear 29 connected to the output shaft 22. A 1st- & Rev brake B.sub.3 and a one-way clutch F.sub.2 are provided in parallel with each other between the carrier 28 and the case 6.
An overdrive brake B.sub.0 is provided between the sun gear 19 and the case 6. Further, an optical or magnetic non-contact type speed sensor 31 is provided on the case 6. The speed sensor 31 detects the rotational speed of the input shaft 12 when the overdrive direct clutch C.sub.0 is engaged, that is, the transmission operates at first, second or third speed.
A rotational speed detection sensor 33 for detecting the rotation of the output shaft 22 is provided to prepare a control parameter for an electronic controller such as ECU or ESC, and a rotational speed detection sensor 34 for obtaining the rotational speed of the output shaft 22 is provided to supply a speed meter with a signal representing the vehicle speed.
In the above-described type of vehicle automatic transmission having a planetary gear unit, a helical gear is ordinarily used as the planetary pinion of the planetary gear unit in consideration of reduction of noise.
Recently, with the development of large and/or high-performance vehicles, a need for improving automatic transmissions with planetary gear units, e.g., increasing the speed change gear ratio, has arisen. To do so, it is necessary to increase the capacity of the planetary gear unit and, hence, to increase the size of the planetary pinion.
A type of planetary pinion 17 having axial cross sections symmetrical in the direction of its rotation axis may be used in the overdrive planetary gear unit 13, as shown in FIG. 2. Since the planetary pinion 17 is constituted by a helical gear as mentioned above, it receives a reaction force f.sub.R0 from the ring gear 21 to produce a reaction force f.sub.R1 in the axial direction of the planetary pinion 17, as shown in FIG. 3, during the operation of the planetary pinion 17, that is, when a torque is input to the carrier to rotate the ring gear 21 by the rotation and revolution of the planetary pinion 17 and to thereby obtain an output from the ring gear 21. On the other hand, the planetary pinion 17 receives a reaction force f.sub.S0 from the sun gear 19, and a reaction force f.sub.S1 is produced in the axial direction of the planetary pinion 17, as shown in FIG. 4. Consequently, the direction of a reaction f.sub.2 resulting from the forces received by the planetary pinion 17 from the ring gear 21 and the direction of a reaction force f.sub.3 resulting from the forces received by the planetary pinion 17 from the sun gear 19 are opposite to each other, as shown in FIG. 5.
The reaction forces f.sub.2 and f.sub.3 cancel out each other because the magnitudes of these forces are equal and these forces act in opposite directions. There is therefore no possibility of the planetary pinion 17 from moving in the axial direction. However, the reaction forces f.sub.2 and f.sub.3 have different points of action, and therefore causes a clockwise torque. That is, the planetary pinion 17 receives a clockwise moment M, as shown in FIG. 6. A force f.sub.MF is thereby applied to a front bearing 102 interposed between the planetary pinion 17 and the pinion shaft 101, while a force f.sub.MR is applied to a rear bearing 103 interposed therebetween.
On the other hand, equal centrifugal forces f.sub.C produced by the revolution of the planetary pinion 17 are applied to the front and rear bearings 102 and 103 in the same direction. Since the direction of application of the force f.sub.MF to the front bearing 102 and the direction of application of the force f.sub.MR to the rear bearing 103 are opposite to each other, the centrifugal force f.sub.C and the force f.sub.MR applied to the rear bearing 103 cancel out each other and the load imposed upon the rear bearing 103 is therefore small, but the magnitudes of the centrifugal force f.sub.C and the force f.sub.MF applied to the front bearing 102 are added to each other and the load imposed upon the front bearing 102 is therefore large.
Where the gear ratio of the overdrive planetary gear unit 13 is increased, the above-mentioned clockwise moment is further increased. Accordingly, the load imposed upon the front bearing 102 becomes much larger than that imposed upon the rear bearing 103. Because the load upon one of the bearings is increased in this manner, there is a possibility of occurrence of pitching.
With respect to the planetary pinion 23 of the front planetary gear unit 14, a similar phenomenon takes place but the relationship between the relating forces is reverse to that in the case of the overdrive planetary gear unit 13. That is, the load imposed upon a rear bearing which supports the planetary pinion 23 is larger than that imposed upon a front bearing which also supports this gear.
This mechanism relating to the planetary pinon 23 of the front planetary gear unit 14 will be described below in detail with reference to FIGS. 7 to 10.
The planetary pinion 23 is also constituted by a helical gear. In a case where the brake B1 is actuated while the clutch C.sub.1 is engaged and the clutch C.sub.2 is disengaged, and where a torque is input through the ring gear 26 to rotate the planetary pinion 23 while revolving the same to output a torque through the carrier 24 and the output shaft 22, the planetary pinion 23 receives a reaction force f.sub.R0 ' from the ring gear 26, and a reaction force f.sub.R2 is produced in the axial direction of the planetary pinion 23, as shown in FIG. 7. On the other hand, the planetary pinion 23 receives a reaction force f.sub.SO ' from the sun gear 25a, and a reaction force f.sub.S2 is produced in the axial direction of the planetary pinion 23, as shown in FIG. 8. Consequently, the direction of a reaction f.sub.4 resulting from the forces received by the planetary pinion 23 from the ring gear 26 and the direction of a reaction force f.sub.5 resulting from the forces received by the planetary pinion 23 from the sun gear 25a are opposite to each other, as shown in FIG. 9.
The reaction forces f.sub.4 and f.sub.5 cancel out each other because the magnitudes of these forces are equal to each other and these forces act in opposite directions. There is therefore no possibility of the planetary pinion 23 from moving in the axial direction. However, the reaction forces f.sub.4 and f.sub.5 have different points of action, and therefore causes a counterclockwise torque. That is, the planetary pinion 23 receives a clockwise moment M', as shown in FIG. 10. A force f.sub.MF ' is thereby applied to a front bearing 202 interposed between the planetary pinion 23 and the pinion shaft 201, while a force f.sub.MR ' is applied to a rear bearing 203 interposed therebetween.
On the other hand, equal centrifugal forces f.sub.C ' produced by the revolution of the planetary pinion 23 are applied to the front and rear bearings 202 and 203 in the same direction. Since the direction of application of the force f.sub.MF ' to the front bearing 202 and the direction of application of the force f.sub.MR ' to the rear bearing 203 are opposite to each other, the centrifugal force f.sub.C and the force f.sub.MF ' applied to the front bearing 202 cancel out each other and the load imposed upon the front bearing 202 is therefore small, but the magnitudes of the centrifugal force f.sub.C ' and the force f.sub.MR ' applied to the rear bearing 203 are added to each other and the load imposed upon the rear bearing 203 is therefore large.